Grounding locations?

[Kanon08]

So I have been in the midst of trying to figure out an ignition problem with my 78 750 for some time now. At first when the bike was just fired up after a long dormancy it was revving strong on all four cylinders, now not the case. First I rebuilt the carbs thinking it was possibly a fuel issue then the coils and wires and now I have come to the conclusion that it must be a bad ground some place. The reason I assume this is after pounding the baffle back into the muffler my running light and cylinders 1 and 4 simultaneously kicked in. Now after having some frame repairs done to the exhaust/passengerer foot peg mount I once again don't have a rear running light although I haven't tried kicking it over yet.

My question is where could this bad ground possibly be? I have checked the what I'm assuming two grounds in the headlight assembly and they seem fine but why would the pounding of the pipe alter the ground? Is there one near the rear brake Master that could have become adjar or something or could I possibly have two separate issues that are coincidentally coinciding together?

If anyone has some imput I'd love to hear it.

Thanks

[tom203]

Pounding on stuff can jar any weak connection- whether on the positive or ground side. Remove tank and make sure you got solid connections at ignition coils,especially coil for 1 and 4. This bike still have points?

[Kanon08]

Oh they are good since I just added some fresh Dyna's to it and the points have been upgraded to a Martek system by the previous owner. Also let's just say it was less of a pound and more of a strong tap.

[MisterCinders]

You must have an open in the tail wire. That wire is always hot once the ignition is on, so isolate what is failing. If your headlight works and your ignition is powered, then you will find the problem in that tail leg of the harness, most likely. The tail-light is the brown wire in that triple plug at the back. It runs all the way to the ignition switch, with a superfluous split off that dead-ends in the head-light bucket (for an option to add running lights, AFAIK).

If you are only missing the tail-light, that brown wire is the culprit. The ground path for that light provides the ground for the brake light and, after about 6 inches, the rear turn signals. If your ground was bad, it would affect the brake-light, at least.

HTH

[Kanon08]

Cool, tanks for the advice. I guess I'll screw with the brown wire a bit more since the running light has been off and on for the last few days. One strange thing is I have hade no issue with the ignition lately, even after a long bumpy ride through the country.....

[Eric]

One thing I have to add is that the brown wire is fed from the grey wire at the ignition switch (the grey wire comes from the headlight switch and powers the gauge lights as well). So, it could be something with that grey wire or ignition switch as well.